Russells: You can mix the two solders you mentioned, assuming by "96s" you meant "96Sn / 4Pb".

If you heat the two tin / lead alloys to a liquid state, you�ll form a tin / lead solution with properties different from either of the two solders. The composition of this new alloy will depend on the amount and composition of the alloys that you are combining. Oh, don�t forget that the metal solderability protection on the leads of each component you are attaching to the board will add third alloy in the mix.

Board fabricators use tin / lead solder for various purposes. One is to protect plating from etching solutions and they routinely strip the solder from boards in their day-to-day operations. They might use nitric acid or acidic ammonium bifluoride-based strippers ... I think the latter is better for tin-lead. Since you are asking this, I would not try this at home, use a "professional driver on a closed course". If you decide to use a professional to do your stripping, of course understand their ability to relevel your boards with 96Sn material you prefer.